Seven out of 10 American voters think the United States can trust the Soviet Union enough to sign a treaty eliminating most of both nations' nuclear weapons by the turn of the century, according to a poll.

Such developments as the Reagan-Gorbachev summits and the Soviet withdrawal from Afghanistan are eroding Americans' longstanding mistrust of the Soviet Union, pollster Daniel Yankelovich said Thursday.But he said six in 10 voters still regard the Soviet Union as "a serious threat" to the United States, and more than a third trust the Soviets "not at all."

The poll was one of several commissioned for "Americans Talk Security," a series of surveys on national defense and security issues.